1. Field of the invention
This invention relates to a combustion chamber of an internal combustion engine, specifically to a compact structure of the combustion chamber.
2. Description of the prior art
In recent years, there has been proposed a compact structure of a combustion chamber in which a recess is formed on a lower portion of a cylinder head which defines an upper portion of the combustion chamber and/or on an upper surface or crown portion of a piston which defines a bottom portion of the combustion chamber so as to obtain a necessary volume without increasing a dimension of an entire structure. Such compact structure of the combustion chamber is advantageous in that a combustion rate of a combustible mixture in the chamber can be improved since a spark generated by an ignition plug can be quickly propagated in the whole chamber.
Japanese Patent Public Disclosure No. 57-198315, laid open to the public on Dec. 4, 1982, discloses a combustion chamber having a recess formed in a cylinder head wherein the recess is provided with a wall portion surrounding an intake and exhaust ports of the chamber to define an intake sub-chamber and an exhaust sub-chamber.
In this combustion chamber disclosed in the Japanese patent publication, an ignition plug is arranged in a recess provided in a boundary portion between the intake and exhaust sub-chambers of the cylinder head.
U.S. Pat. No. 3,766,900, German Patent No. 1,801,765 and English Patent No. 640,734 disclose compact structures of the combustion chamber.
With the above structure of combustion chamber as disclosed in the Japanese patent publication, it should however be noted that a combustible mixture cannot be supplied sufficiently around the ignition plug during a compression stage causing a deterioration of a flame propagation. In addition, an exhaust gas tends to stay around the ignition plug during an intake stage and a hydrocarbon compound may deposit on the plug because of a poor scavenging effect so that a combustion property may be eventually deteriorated.